Submission #993654

#	Time	Username	Problem	Language	Result	Execution time	Memory
993654		danikoynov	Wells (CEOI21_wells)	C++14	0 / 100	1 ms	604 KiB

wells

#include<bits/stdc++.h>
#define endl '\n'

using namespace std;
typedef long long ll;

void speed()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}

const int maxn = 1e4 + 10;

int n, k;
vector < int > adj[maxn];

void input()
{
    cin >> n >> k;
    for (int i = 1; i < n; i ++)
    {
        int v, u;
        cin >> v >> u;
        adj[v].push_back(u);
        adj[u].push_back(v);
    }
}

int used[maxn];
void bfs(int s)
{
    for (int i = 1; i <= n; i ++)
        used[i] = -1;
    queue < int > q;
    q.push(s);
    used[s] = 0;
    while(!q.empty())
    {
        int v = q.front();
        q.pop();
        for (int u : adj[v])
        {
            if (used[u] == 0)
            {
                used[u] = used[v] + 1;
                q.push(u);
            }
        }
    }
}

int tin[maxn], ord[2 * maxn], timer;
int depth[maxn];
void dfs(int v, int p)
{
    ord[ ++ timer] = v;
    tin[v] = timer;
    for (int u : adj[v])
    {
        if (u == p)
            continue;

        depth[u] = depth[v] + 1;
        dfs(u, v);
        ord[++ timer] = v;
    }
}

const int maxlog = 23;
int dp[maxlog][2 * maxn], lg[2 * maxn];
void build_sparse_table()
{
    for (int i = 1; i <= timer; i ++)
    {
        lg[i] = lg[i / 2] + 1;
        dp[0][i] = ord[i];
    }

    for (int j = 1; j < lg[timer]; j ++)
    {
        for (int i = 1; i <= timer - (1 << j) + 1; i ++)
        {
            dp[j][i] = dp[j - 1][i + (1 << (j - 1))];
            if (depth[dp[j - 1][i]] < depth[dp[j][i]])
                dp[j][i] = dp[j - 1][i];
        }
    }

    /** for (int j = 0; j < lg[timer]; j ++, cout << endl)
         for (int i = 1; i <= timer - (1 << j) + 1; i ++)
         cout << dp[j][i] << " ";*/
}

int lca(int v, int u)
{
    int l = tin[v], r = tin[u];
    if (l > r) swap(l, r);
    int len = lg[r - l + 1] - 1;
    int lca = dp[len][r - (1 << len) + 1];
    if (depth[dp[len][l]] < depth[lca])
        lca = dp[len][l];
    return lca;
}

int dist(int v, int u)
{
    return depth[v] + depth[u] - 2 * depth[lca(v, u)];
}

int path[maxn][maxn];
void find_path()
{
    for (int i = 1; i <= n; i ++)
    {
        bfs(i);
        for (int j = 1; j <= n; j ++)
            path[i][j] = used[j] - 1;
    }
}
vector < int > st;

int marked[maxn], forb[maxn];


void bfs_again(int v)
{
    for (int i = 1; i <= n; i ++)
        marked[i] = 0;
    queue < int > q;
    q.push(v);
    marked[v] = 1;
    while(!q.empty())
    {
        int v = q.front();
        q.pop();

        for (int u : adj[v])
        {
            if (!marked[u] && !forb[u])
            {
                marked[u] = marked[v] + 1;
                q.push(u);
            }
        }
    }
}
void check()
{

    for (int s = 1; s <= n; s ++)
    {

        bfs(s);
        st.clear();
        for (int i = 1; i <= n; i ++)
            forb[i] = 0;
        for (int i = 1; i <= n; i ++)
        {
            if (used[i] % k == 0)
            {
                forb[i] = 1;
                st.push_back(i);
            }
        }

        /**cout << "---------" << endl;
        for (int cur : st)
            cout << cur << " ";
        cout << endl;*/

        bool done = true;
        for (int v : st)
        {
            if (!done)
                break;
            for (int u : st)
            {

                if (v != u && dist(v, u) < k)
                {
                    ///cout << "dist " << lca(v, u) << " " << v << " " << u << endl;
                    done = false;
                    break;
                }
            }
        }



        for (int i = 1; i <= n; i ++)
        {
            if (forb[i])
                continue;



            bfs_again(i);
            int mx = 1;
            for (int i = 1; i <= n; i ++)
                if (marked[i] > marked[mx])
                    mx = i;
            if (marked[mx] >= k)
            {
                done = false;
                break;
            }
            bfs_again(mx);
            int len = 0;
            for (int i = 1; i <= n; i ++)
                if (marked[i] > len)
                    len = marked[i];
            //cout << "from " << i << endl;
            //cout << "len " << len << endl;
            if (len >= k)
            {
                done = false;
                break;
            }

        }
        ///cout << "fine " << i << endl;
        if (done)
        {
            cout << "YES" << endl;
            cout << 0 << endl;
            return;
        }
    }

    cout << "NO" << endl;
    cout << 0 << endl;
}
void solve()
{
    input();
    dfs(1, -1);
    build_sparse_table();
    ///find_path();
    ///cout << dist(2, 6) << endl;
    check();

}

int main()
{
    ///speed();
    solve();
    return 0;
}
/**
11 4
1 2
2 3
3 4
4 5
4 6
3 7
7 8
3 9
9 10
10 11
*/

• Subtask 1: 0 / 30
• Subtask 2: 0 / 20
• Subtask 3: 0 / 20
• Subtask 4: 0 / 30